In recent years, hybrid cars using both an internal combustion engine and a motor have been rapidly prevailing in order to improve the fuel efficiency of the cars. On the other hand, electric cars that can travel using only a motor have been increasingly commercialized. Realization of these cars needs a power conversion apparatus provided between a battery and a motor to convert DC power into AC power and vice versa.
A well-known power conversion apparatus for hybrid cars comprises two inverters for driving a driving moor and a power generator and a DC-DC converter for boosting a power supply voltage. The inverters and the DC-DC converter use, as switching elements, semiconductor modules using IGBTs (Insulated Gate Bipolar Transistors). Among the components of the inverters and the DC-DC converter, the semiconductor modules generate a particularly large amount of heat. High performance is needed for a cooler that cools the semiconductor modules.
In general, a water-cooling cooler is used which uses, for example, water as a cooling medium. With a focus on the concentrated effects of heat generated by a semiconductor module installed on an upstream side of a refrigerant channel in the cooler on a semiconductor module installed on a downstream side of the refrigerant channel, a cooling structure has been proposed which avoids degradation of the cooling performance of the downstream semiconductor module.